The present invention relates to a method for regulating the pressure in the intake duct of an internal combustion engine having an exhaust turbocharger and a control unit configured to determine a desired pressure value as a function of the current load, comprising the steps of setting current pressure in the intake duct via a valve to the desired pressure value to be set, and actuating the valve as a function of an actuating signal produced by the control unit. The present invention also relates to an apparatus for carrying out the foregoing method, which has a throttle valve in the intake duct, an exhaust turbocharger arranged in an exhaust line, a bypass valve, a bypass conduit arranged to be shut off by the bypass valve and to bypass the turbocharger, and a control unit configured to effect a load-dependent setting of the throttle valve and the bypass valve.
DE 39 39 754 A1 describes an internal combustion engine with an exhaust turbocharger having a turbine driven by the stream of exhaust gas and driving a compressor in the intake duct. The turbine in the exhaust line is bypassed by a bypass conduit, which can be shut off by a bypass valve. The regulation of the intake duct pressure to a specified desired pressure value is accomplished by adjusting a throttle valve in the intake duct and by actuating the bypass valve. Thereby, the stream of exhaust gas fed to the turbine of the exhaust turbocharger can be adjusted. The position of the throttle valve and of the bypass valve is determined by a control unit as a function of the load state of the internal combustion engine. For this purpose, actuating signals for actuating drives assigned to the throttle valve and the bypass valve are produced in a control unit. In order to adjust the pressure in the intake duct to the intended desired value, the throttle valve is first of all pivoted in the direction of complete opening of the intake duct in the low-load range of the internal combustion engine. If a further pressure rise in the intake duct is required even after the maximum throttle-valve open position has been reached, the bypass valve is moved as a function of the load by the control unit from its open position up to that time into its closed position. As the load increases, the bypass conduit is therefore shut off, so that an increasing stream of exhaust gas impinges on the turbocharger. This allows a higher desired pressure to be achieved in the intake duct.
Depending on the load state of the internal combustion engine, the controller implemented in the control unit acts upon either the throttle-valve position or the position of the bypass valve. In the transitional range from part load to full load of the internal combustion engine, only a limited dynamic response of the pressure build-up in the intake duct can thereby be achieved. The sequential actuation of the throttle valve and the bypass valve, owing to the common controller for both valve devices, results in an unavoidable regulation delay. Because of the intrinsic dynamic response of the throttle valve and the bypass valve, there is a delay upon each transition of the actuation of one of the two valve devices. It is furthermore disadvantageous that the controller can only be set in an optimum manner for one of the two valve devices. Consequently, optimum regulation of the other valve is impossible.
An object of the present invention is to provide a method and an apparatus for building up the pressure in the intake duct of an internal combustion engine with a suitable dynamic response for each load state, particularly when using a number of valve devices.
According to the invention, this object has been achieved with a method in which the actuating signal is taken as a control signal, as a function of a corrected relative desired pressure value, from a control characteristic map stored in the control unit. When required, a controller signal produced in a controller, in which one input variable is a signal formed from adding the current pressure and the desired value to be set, is superimposed on the control signal. The apparatus for carrying out the foregoing method has a desired-value transmitter and a controller unit, the latter having a switching-signal transmitter, a switching element, a memory with respective control characteristic maps for the throttle valve and the bypass valve and respective controllers, each of which is independently activatable as a function of predetermined switching criteria by the switching-signal transmitter and the switching element.
According to the method of the present invention, adjustment of the pressure in the intake duct is performed by control with superimposed regulation. The actuating signal is made up of a control signal, which is taken from a control characteristic map as a function of a corrected desired pressure value, and of a controller signal, which is superimposed on the control signal as required, in order to achieve exact setting of the pressure to the intended desired value. The permanently active controller ensures that the valve device is supplied continuously with an actuating signal and there are thus no delays due to a dynamic response of the valve device. The control signal can be matched specifically to the dynamic response of the valve device. The superimposed regulation which is switched in as required ensures that the specified desired pressure value can be set exactly and without steady-state error.
A second valve device can be provided for regulating the intake pressure. A second actuating signal independent of the first actuating signal is advantageously produced by the control unit and is taken from a second control characteristic map tailored to the second valve device. This second control signal can, in turn, have a dedicated controller signal superimposed thereon, with the controller signal being produced in a second controller. The controller signals of the first and the second controllers are completely independent and it is advantageous, depending on the load applied, for only one of the two controllers to be activated. One of the two controllers can be activated by a switching signal dependent on the specified desired pressure value. The first controller is preferably assigned to the part-load range and the second controller to the full-load range.
Each of the two controllers is assigned a control characteristic map with a control signal taken from it which acts continuously on the valve devices. Consequently, both valve devices can be operated independently of one another in the transitional range between part load and full load. This provides a favorable dynamic pressure build-up in the intake duct. Also, the separate regulation allows determination of the regulation parameters in a manner matched to the respective valve device.
The calculation of the desired pressure value preferably includes characteristics such as the engine speed and the power demand by the driver. These variables characterize the load state of the internal combustion engine. Ambient conditions such as the ambient air pressure, the temperature of the intake air and the temperature of the cooling water can be included as further influencing variables. All the influencing variables can be defined in the form of characteristic maps, and a plurality of characteristic maps can be provided for each influencing variable. These maps are assigned to the various load ranges of the internal combustion engine. The respective characteristic map is activated by a switching signal which reflects the load state of the internal combustion engine. A PI controller signal is advantageous in this regard because there is no remaining steady-state system error.
The desired pressure value is fed to a switching-signal transmitter in which a hysteresis curve is implemented as a switching curve for the load-dependent activation of one of the two controllers. The hysteresis curve lies between a lower and an upper pressure limit value. A switched change between the controllers takes place when the desired pressure value reaches one of the two limit values.
As an additional condition, a switched change can also take place when the controller signal either of the first or second controller exceeds or undershoots a specified controller limit value. This additional switching condition ensures that the desired intake-pipe pressure is achieved in all cases, even if individual engine components are not operating correctly, as a result of, for example, soiling or contamination. The additional switching condition ensures that a switch is made to the controller for the higher load range in time to reach the desired pressure, even if this is not necessary according to the switching curve stored in the switching-signal transmitter.
The apparatus for carrying out the above-described method includes a throttle valve in the intake duct as the first valve device and a bypass valve in the bypass conduit which bypasses the turbocharger as the further valve device. The control unit which supplies the actuating signals for the regulation of the throttle valve and the bypass valve includes a desired-value transmitter for determining the desired pressure value and a controller unit. The controller unit comprises a memory with respective control characteristic maps for the throttle valve and the bypass valve, and respective controllers.
The controllers can be activated by a switching-signal transmitter and a switching element which are likewise part of the controller unit.